Convert Lead Automatically Using Trigger:-

Scenario:- Convert Lead Automatically when Convert_Now__c check box is true in Lead record.

Step 1:- Create Convert_Now__c check box custom field in Lead object

Step 2:- Write a Trigger in Lead object

trigger convert_Lead on Lead (after insert,after update) {

    for(Lead led : Trigger.New){

        Lead ledold=Trigger.Isinsert?new Lead() : trigger.oldmap.get(led.id);

        if(led.Convert_Now__c!=ledold.Convert_Now__c && led.Convert_Now__c==true){

            Database.LeadConvert lc = new database.LeadConvert();

            lc.setLeadId(led.id);

            LeadStatus convertStatus = [SELECT Id, MasterLabel FROM LeadStatus WHERE IsConverted=true LIMIT 1];

            lc.setConvertedStatus(convertStatus.MasterLabel);

            Database.convertLead(lc);

        }

    }

}

The Above Trigger Converts the Lead Record when Convert_Now__c check box is true.